It is standard commercial practice to provide several versions of the same basic computer, each version having different technical characteristics adapted to the needs of a particular group of users. Thus, for desktop computers, the provision of a graphics accelerator card may be essential for certain users but not for other users; to meet the demands of both types of users, a computer manufacturer may therefore provide one version of a computer with a graphics accelerator card and appropriate software, and a second version without the card (but generally with an expansion card slot enabling a user later to add a graphics accelerator card if so desired).
Generally, for desktop computers there are two types of optional units that can be included in a computer to enhance the basic design, these two types being an expansion card and a mass storage drive assembly. FIG. 1 shows an expansion card 10 provided with a standard edge connector portion 11 intended to plug into a standard edge connector provided in the computer, and a mounting plate 12 that can be secured by a fixing screw or other suitable means to a housing wall of the computer. Where the expansion card 10 is provided with external connectors, these project out from the mounting plate 12 to be accessible through an access aperture formed in the housing wall of the computer. The dimensions and electrical characteristics of expansion cards are usually well defined. The mounting zone and mounting elements provided in the computer for receiving an expansion card are frequently referred to as an "expansion card slot".
FIG. 2 depicts a mass storage drive unit here illustrated as a hard disc drive 15. Other forms of mass storage drive include floppy disc drives, CD-ROM drives and tape drives. All generally conform to particular size formats and are provided with standard fixing means (typically a series of threaded apertures 16 for receiving fixing screws by which the drive unit can be mounted in a metal mounting cage forming part of the basic support structure of the computer). Electrical connection to such drive units is usually provided by way of flying leads and one or more connectors that plug into the drive unit. The mounting zone and mounting elements provided in the computer for receiving a drive unit are frequently referred to as a "drive bay".
To provide both the manufacturer and user with the flexibility to add optional units as needed, it is now common practice to provide several expansion card slots and drive bays in a computer. The manufacturer populates the slots and bays according to the version of the computer to be produced whilst a user can add additional units as desired. However, an unused expansion slot or drive bay effectively represents unnecessary expense not only because of the obvious use of extra materials for the mounting elements and the larger housing size needed to accommodate the slot or bay, but also because the cooling and power supply systems of the computer must be designed for the case of all slots and bays being populated. There is therefore a tradeoff between providing extra slots and bays to increase flexibility and keeping their number down to reduce unnecessary costs. In addition, aesthetic considerations regarding the external size and shape of the computer (important in the home computer market), place a limit on the number of slots and bays that can be put in a computer.
It is an object of the invention to ease this conflict between flexibility and cost.